The present invention relates to a chip-type capacitor having a resin-encapsulated structure, a method of manufacturing the same and a molding die.
An existing chip-type capacitor of the type includes a capacitor element, an anode terminal, a cathode terminal, and an encapsulation resin covering these components.
A capacitor element is produced by preparing powder of a valve action metal, burying an anode lead wire in the powder with its one end led out from the powder, molding and sintering the powder to form a porous anode body, forming a dielectric oxide film on the anode body by a known technique, and successively forming, on a surface of the dielectric oxide film, an electrolyte layer and a cathode layer. Furthermore, the anode terminal has a base portion having a bottom surface exposed on a mounting surface of the encapsulation resin and a standing-up portion perpendicular to the base portion. The anode lead wire led out from the capacitor element is connected to the standing-up portion of the anode terminal by a known technique such as laser welding. On the other hand, the cathode terminal is connected and fixed through a conductive adhesive to the cathode layer of the capacitor element so that a bottom surface of the cathode terminal is exposed on the mounting surface of the encapsulation resin. The encapsulation resin is formed by transfer molding so as to cover an entirety of the capacitor element and a connecting portion between the capacitor element and each of the anode and the cathode terminals. The encapsulation resin, together with the anode and the cathode terminals, is cut into a desired outer dimension by, for instance, dicing. Thus, the chip-type capacitor is formed.
The existing chip-type capacitor is simple in connecting structure between the capacitor element and each of the anode and the cathode terminals. It is therefore possible to improve an accommodation volume efficiency of the capacitor element with respect to the encapsulation resin. Accordingly, the chip-type capacitor can be reduced in size and thickness and yet large in capacity so as to meet the recent demand for a small-sized, thin-profile, and light-weight portable equipment, such as a mobile telephone.
In the above-mentioned existing chip-type capacitor, sections of the anode and the cathode terminals are exposed on the side surfaces of the capacitor. When the capacitor is mounted on a substrate, a plating process for plating the sections of the anode and the cathode terminals must be carried out in order to assure wetting-up (hereinafter referred to as a “fillet”) of a solder over the sections of the anode and the cathode terminals. The application of the plating process results in an increase in production cost and production time (lead-time). Furthermore, there arises a problem that, if a liquid leaks into the inside of the encapsulation resin during a series of plating processes such as degreasing, plating, cleaning and rust-proofing, the electric characteristics and the reliability of the capacitor will be deteriorated.
In mounting of the chip-type capacitor, it is general that the capacitor is mounted on a land formed on the substrate and thereafter soldered by reflow soldering. At that time, due to the surface tension of the solder, a so-called Manhattan phenomenon or Tombstone phenomenon is often caused to occur in which one of the terminals stands up from the substrate to be perpendicular thereto. In particular, such phenomenon is more likely to occur in a smaller-size and lighter-weight tiny chip. It is therefore essential and indispensable to form a fillet which serves to improve the stability of a mounting posture.
In order to solve the above-mentioned problems, JP-A Nos. 2001-291641 and 2002-43175 (hereinafter will be called as References 1 and 2, respectively) propose methods of forming a fillet without performing the plating process after the terminals are cut.
In the method disclosed in Reference 1, each of an anode terminal and a cathode terminal is provided with a terminal bending portion so as to allow a solder to enter into a space under the bending portion, thereby forming a fillet.
In the method disclosed in Reference 2, a part of the anode and the cathode terminal is raised to form a terminal standing-up portion, which is exposed on an outer surface of the encapsulation resin, and the fillet is formed at the standing-up portion.
However, in the chip-type capacitors described in References 1 and 2, a lead frame (strip-like metal plate) must be preliminarily subjected to complicated processing in order to execute micro-bending of a part of each terminal. This results in an increase in production cost. Since the surface of each of the terminal bending portion and the terminal standing-up portion is not clamped by an upper die and a lower die of a molding die and is not pressed, the resin is likely to intrude and adhere to the surface of the terminal. Such intrusion and adhesion of the resin is one of factors preventing the formation of the fillet when the capacitor is mounted on the substrate.
Furthermore, in order to prevent the adhesion of the resin, it is necessary to introduce an additional production step, such as a step of sticking a masking tape to the terminal, a horning step after the molding. This results in an increase in production cost. After the mounting, the fillet is formed inwardly from the outer contour of the capacitor so that the visibility from the above is poor. Particularly upon mounting with a high density, inspection is difficult after the capacitor is mounted on the substrate.